1. The Carbon Farming Initiative and Agricultural Emissions This presentation was prepared by the University of Melbourne for the Regional Landcare Facilitator training funded through the Australian Government’s Carbon Farming Initiative Communications Program

2. This presentation explains the nitrogen cycle in agricultural production systems and the various pools of nitrogen PART 3: THE NITROGEN CYCLE IN AGRICULTURAL SYSTEMS

3. The nitrogen cycle Content –The nitrogen cycle in agricultural systems –Fluxes between nitrogen pools –Forms of nitrogen and their fate

4. The nitrogen cycle Whitehead 1995

5. The nitrogen cycle Atmosphere –N 2 (nitrogen) 78% of the atmosphere –O 2 = 21%, CO 2 = 0.04% Fixed by legumes into plants and soil –N 2 O (nitrous oxide) 0.32 ppm (0.00003%) Eckard 2011

6. The nitrogen cycle Main forms of soil & plant N –NH 3 – Ammonia Organic matter Fertilisers –Urea, DAP, UAN etc. Major source of plant N Eckard 2011 oxygen amide ion

7. The nitrogen cycle Main forms of soil & plant N –NH 4 + – Ammonium Soil solution Loosely bound on cation exchange –Positive charge attached to clay »Exchangeable »Clay-fixed (non-exchangeable) »Does not readily leach Major source of plant N (nitrogen) –Preferential uptake in colder, wetter soils Rapidly converts to NO 3 - (nitrate ion) –In warm, well-drained soils Eckard 2011

8. The nitrogen cycle Main forms of soil & plant N –NO 3 (nitrate ion) Major source of plant nutrition –Drier soils Accumulates in some plants –e.g. Brassicas, annual ryegrass, kikuyu, cereal grains –Breaks down to NO 2 in rumen – toxicity Soluble in water – leaches –NO 2 (nitrite ion) Transient in plants and soils Main form of toxicity in ruminants Eckard 2011

9. The nitrogen cycle Main forms of soil & plant N –Soil organic matter N Decomposed residues –Amides, proteins etc Microorganisms (microbial biomass) C: N ratio –Usually 10:1 to 40:1 Major source of plant N –Through mineralisation Eckard 2011

10. The nitrogen cycle Mineralisation –Microbial breakdown of soil organic matter to ammonium –The main mechanism for supplying N to plants Nitrification –Microbial conversion of ammonium to nitrate Ammonia sources –Urine, decaying organic matter, fertiliser Warm, moist (not waterlogged) soils Denitrification –Microbial conversion of nitrate to N 2 and N 2 O gasses Warm, waterlogged soils N 2 O is a powerful greenhouse gas Immobilisation –Microbial assimilation of soil nitrogen into OM OM NH 4 + NO 3 - N2N2 N2ON2O Eckard 2011 organic matter ammonium ion nitrous oxidenitrogen nitrate ion

11. The nitrogen cycle Nitrogen balances in Agricultural systems –Biological efficiency Less than 50% N InputsDairyGrains N fertiliser15090 N 2 fixation800 Atmosphere88 Feed450 Total Input28398 N output in product Milk80 Meat8 Grain 40 Total Outputs8840 N Surplus19558 Efficiency (%)3141 Eckard et al 2007